Methods for inhibiting hydrate blockage in oil and gas pipelines using amide compounds

ABSTRACT

A method and an amide composition used therein for inhibiting, retarding, mitigating, reducing, controlling and/or delaying formation of hydrocarbon hydrates or agglomerates of hydrates. The method may be applied to prevent or reduce or mitigate plugging of conduits, pipes, transfer lines, valves, and other places or equipment where hydrocarbon hydrate solids may form under the conditions. At least one amide compound is added into the process stream, where the compound may be mixed with another compound selected from amino alcohols, esters, quaternary ammonium, phosphonium or sulphonium salts, betaines, amine oxides, other amides, simple amine salts, and combinations thereof.

This application claims priority of U.S. provisional patent application60/513,311 filed on Oct. 21, 2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the prevention of gas hydrate blockage in oiland natural gas pipelines containing low-boiling hydrocarbons and water.More specifically, the invention relates to a method of controlling gashydrate blockage through the addition of various chemical compositions.

2. Background of the Related Art

When hydrocarbon gas molecules dissolve in water, the hydrogen-bondednetwork of water molecules encapsulates the gas molecules to form acage-like structure or hydrate. Higher pressures and lower temperaturesfoster the formation of these structures. These hydrates grow byencapsulating more and more gaseous molecules to form a crystallinemass. The crystalline mass agglomerates to form a larger mass that canresult in a plugged transmission line. The hydrocarbon gases that formthe majority of the hydrates include methane, ethane, propane, n-butane,iso-butane, n-pentane, iso-pentane, and combinations of these gases.

Thermodynamic hydrate inhibitors, such as methanol or one of theglycols, have traditionally been used to prevent these hydrateformations. These thermodynamic inhibitors are effective at 5-30% (orhigher) based on the amount of water. As oil companies are exploring newproduction in deep waters, the total gas/oil/water productions are alsoincreasing. The use of these thermodynamic inhibitors is not viable inthese applications due to logistics.

Kinetic hydrate inhibitors have been identified to prevent these hydrateformations so that the fluids can be pumped out before a catastrophichydrate formation occurs. The kinetic inhibitors prevent or delayhydrate crystal nucleation and disrupt crystal growth. These kinetichydrate inhibitors contain moieties similar to gas molecules previouslymentioned. It is suspected that these kinetic inhibitors prevent hydratecrystal growth by becoming incorporated into the growing hydratecrystals, thereby disrupting further hydrate crystal growth. The growinghydrate crystals complete a cage by combining with the partialhydrate-like cages around the kinetic hydrate inhibitor moietiescontaining gas-like groups. These inhibitors are effective with orwithout the presence of a liquid hydrocarbon phase, but they aretypically less effective in preventing the hydrate formation as theproduction pressure increases. Examples of kinetic hydrate inhibitorsinclude poly(N-methylacrylamide), poly(N,N-dimethylacrylamide),poly(N-ethylacrylamide), poly(N,N-diethylacrylamide),poly(N-methyl-N-vinylacetamide), poly(2-ethyloxazoline),poly(N-vinylpyrrolidone), and poly(N-vinylcaprolactam).

Unlike the kinetic hydrate inhibitors, anti-agglomerate hydrateinhibitors are effective only in the presence of an oil phase. Theseinhibitors do not inhibit the formation of gas hydrates to the samelevel as kinetic inhibitors, rather their primary activity is inpreventing the agglomeration of hydrate crystals. The oil phase providesa transport medium for the hydrates which are referred to as hydrateslurries so that the overall viscosity of the medium is kept low and canbe transported along the pipeline. As such, the hydrate crystals formedin the water-droplets are prevented from agglomerating into a largercrystalline mass.

Examples of several chemicals acting as anti-agglomerate hydrateinhibitors have been reported in U.S. Pat. Nos. 5,460,728; 5,648,575;5,879,561; and 6,596,911. These patents teach the use of quaternaryammonium salts having at least three alkyl groups with four or fivecarbon atoms and a long chain hydrocarbon group containing 8-20 atoms.Exemplary compositions include tributylhexadecylphosphonium bromide andtributylhexadecylammonium bromide.

More specifically, Klomp (U.S. Pat. No. 5,460,728) teaches the use ofalkylated ammonium, phosphonium or sulphonium compounds having three orfour alkyl groups in their molecule, at least three of which areindependently chosen from the group of normal or branched alkyls havingfour to six carbon atoms. Klomp (U.S. Pat. No. 5,648,575) teaches verysimilar compositions having three or four organic groups in theirmolecule, at least three of which have at least four carbon atoms, i.e.,two normal or branched alkyl groups having at least four carbon atomsand with a further organic moiety containing a chain of at least fourcarbon atoms. Klomp (U.S. Pat. No. 5,879,561) teaches the use ofalkylated ammonium or phosphonium compounds having four alkyl groups,two of which are independently normal or branched alkyls having four orfive carbon atoms and two more of which independently represent organicmoieties having at least eight carbon atoms.

Klug (U.S. Pat. No. 6,369,004 B1) teaches the kinetic inhibition of gashydrate formation using polymers based on reacting maleic anhydride withone or more amines. These polymers can also be used together withvarious other substances, called synergists, includingtetrabutylammonium salts, tetrapentylammonium salts, tributylamineoxide, tripentylamine oxide, zwitterionic compounds having at least onebutyl or pentyl group on the quaternary ammonium nitrogen atom, such asas Bu₃N⁺—CH₂—COO⁻. However, kinetic inhibitors are not effective as thepipeline pressure increases.

Rabeony (U.S. Pat. No. 6,015,929) teaches the use of specificzwitterionic compounds such as R(CH₃)₂N⁺—(CH₂)₄—SO₃ ⁻ asanti-agglomerate hydrate inhibitors. The synthesis of this productinvolves the use of butyl sultone.

However, there remains a need for hydrate inhibitor compounds thateffectively prevent agglomeration of hydrates in oil and gastransportation and handling processes. It would be desirable to identifyhydrate inhibitor compounds that are effective at higher pressuresand/or lower temperatures such as those encounter in deep waterproduction. It would be even more desirable if the same compounds hadincreased biodegradability.

SUMMARY OF THE INVENTION

Further still, the method may include adding to the mixture an effectiveamount of at least one amide compound having a formula:

where: R₁, R₂, R₄, and R₅ are organic moieties; R₁ is an alkyl havingfrom 4 to 5 carbon atoms; R₂ is hydrogen or an alkyl having from 1 to 4carbon atoms; R₄ is selected from —(CH₂)_(t)-, —[CH₂—CHR₆)_(t)]-,—(CH₂—CHR₆O)_(u)—(CH₂)_(t)— and combinations thereof; wherein t is aninteger 2 to 4, u is 0 or an integer (1 or greater) and R₆ is hydrogenor an alkyl having from 1 to 3 carbon atoms; R₅ is an organic moiety,for example an alkyl or alkenyl group, having 4 to 20 carbon atoms; A isN or P; X⁻ is an anion; and a is 0 or 1. When a is 0, then R₃ isselected from —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻,—[(CH₂CH(OH)CH₂)—(SO₂)]—-O⁻, —[(CH₂)_(n) —(C═S)]—S⁻ and combinationsthereof, wherein b is 0 or 1, c is 0 or 1, and R₆ is selected fromhydrogen and methyl. When a is 1, then R₃ is selected from hydrogen,organic moieties having from 1 to 20 carbon atoms, and combinationsthereof. Preferably, R₃ is the same as the group containing the amidefunctionality.

The X⁻ anion is preferably selected from hydroxide, carboxylate, halide,sulphate, organic sulphonate, and combinations thereof. Suitable halideions include, without limitation, bromide, chloride, and combinationsthereof.

In one embodiment, R₃ is hydrogen, a is 1, and the anion X⁻ is selectedfrom hydroxide, carboxylate, halide, sulphate, organic sulphonate, andcombinations thereof. In a still further embodiment, the at least oneamide compound is the reaction product of an N,N-dialkyl-aminoalkylaminewith an ester or glyceride. Preferably, the ester or glyceride isderived from a plant source or an animal source, selected from coconutoil, tallow oil, vegetable oil, and combinations thereof.

The method may further comprise adding at least one amine salt to themixture along with the at least one compound. Suitable amine saltsinclude those previously described herein. Furthermore, the at least onecompound may be mixed with the solvents previously described herein.

In another embodiment, the at least one compound includes a productprepared by the reaction of an amine selected from(3-dialkylamino)propylamine and (3-dialkylamino)ethylamine withvegetable oil or tallow oil followed by reacting with a reactantselected from an organic halide, such as an alkyl halide, having from 4to 20 carbon atoms, hydrogen peroxide, and an acid, wherein the acid isselected from mineral acids, formic acid, acetic acid, chloroaceticacid, propionic acid, acrylic acid, and methacrylic acid, and whereinthe dialkyl of the (3-dialkylamino)propylamine includes two alkyl groupsindependently selected from methyl, ethyl, propyl, butyl, morpholine,piperidine, and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of a temperature and pressure profile used in FIGS.3-17.

FIG. 2 is a graph of sensor activation time (a measure of hydrateformation and blockage ) as a function of time for an untreated mixtureof hydrocarbon and water.

FIG. 3 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% trimethylhexadecylammoniumbromide.

FIG. 4 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% dimethylethylhexadecylammoniumbromide

FIG. 5 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% dimethylbutylhexadecylammoniumbromide.

FIG. 6 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% dimethylbutyloctadecylammoniumbromide.

FIG. 7 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% dipropylbutylhexadecylammoniumbromide.

FIG. 8 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% dibutylpropylhexadecylammoniumbromide.

FIGS. 9 a and 9 b are graphs of sensor activation time (a measure ofhydrate formation or blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% and 1% tributylhexadecylammoniumbromide, respectively.

FIG. 10 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% dimethyldihexadecylammoniumbromide.

FIG. 11 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% N,N-dibutyl-cocoamidopropylcarbomethoxy betaine.

FIG. 12 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3%N,N-dibutylamino-cocoamidopropylamine oxide.

FIG. 13 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3%N,N,N-tributyl-cocoamidopropylammonium bromide.

FIG. 14 is a graph of sensor activation time (a measure of hydrateformation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3%N,N-dibutylhexadecyl-cocoamidopropylammonium bromide.

FIGS. 15 a and 15 b are graphs of sensor activation time (a measure ofhydrate formation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% and 1%N,N-dibutylhexadecyltriethoxyammonium bromide, respectively.

FIGS. 16 a and 16 b are graphs of sensor activation time (a measure ofhydrate formation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% and 1%tributylhexadecylphosphonium bromide, respectively.

FIGS. 17 a and 17 b are graphs of sensor activation time (a measure ofhydrate formation and blockage) as a function of time for a mixture ofhydrocarbon and water treated with 3% and 1%, respectively, of a blendof N,N-dibutyl-cocoamidopropyl carboethoxy betaine and amine salt.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

This invention relates a method and a composition used therein forinhibiting, retarding, mitigating, reducing, controlling and/or delayingformation of hydrocarbon hydrates or agglomerates of hydrates. Themethod may be applied to prevent or reduce or mitigate plugging ofconduits, pipes, transfer lines, valves, and other places or equipmentwhere hydrocarbon hydrate solids may form under the conditions.

The term “inhibiting” is used herein in a broad and general sense tomean any improvement in preventing, controlling, delaying, reducing ormitigating the formation, growth and/or agglomeration of hydrocarbonhydrates, particularly light hydrocarbon gas hydrates in any manner,including, but not limited to kinetically, thermodynamically, bydissolution, by breaking up, other mechanisms, or any combinationsthereof.

The term “formation” or “forming” relating to hydrates is used herein ina broad and general manner to include, but are not limited to, anyformation of hydrate solids from water and hydrocarbon(s) or hydrocarbongas(es), growth of hydrocarbon hydrate solids, agglomeration ofhydrocarbon hydrates, accumulation of hydrocarbon hydrates on surfaces,any deterioration of hydrate solids plugging or other problems in asystem and combinations thereof.

The present method is useful for inhibiting hydrate formation for manyhydrocarbons and hydrocarbon mixtures. The method is particularly usefulfor lighter or low-boiling, C₁-C₅, hydrocarbon gases or gas mixtures atambient conditions. Non-limiting examples of such “low-boiling” gasesinclude methane, ethane, propane, n-butane, isobutane, isopentane andmixtures thereof. Other examples include various natural gas mixturesthat are present in many gas and/or oil formations and natural gasliquids (NGL). The hydrates of all of these low-boiling hydrocarbons arealso referred to as gas hydrates. The hydrocarbons may also compriseother compounds including, but not limited to CO₂, hydrogen sulfide, andother compounds commonly found in gas/oil formations or processingplants, either naturally occurring or used in recovering/processinghydrocarbons from the formation or both, and mixtures thereof.

The method of the present invention involves contacting a hydrocarbonand water mixture with a suitable compound or composition. When aneffective amount of the compound is used, hydrate blockage is prevented.In the absence of such effective amount, hydrate blockage is notprevented.

The contacting may be achieved by a number ways, including mixing,blending with mechanical mixing equipment or devices, stationary mixingsetup or equipment, magnetic mixing or other suitable methods, otherequipment and means known to one skilled in the art and combinationsthereof to provide adequate contact and/or dispersion of the compositionin the mixture. The contacting can be made in-line or offline or both.The various components of the composition may be mixed prior to orduring contact, or both. As discussed, if needed or desired, thecomposition or some of its components may be optionally removed orseparated mechanically, chemically, or by other methods known to oneskilled in the art, or by a combination of these methods after thehydrate formation conditions are no longer present.

Because the present invention is particularly suitable for lower boilinghydrocarbons or hydrocarbon gases at ambient conditions, the pressure ofthe condition is usually at or greater than atmospheric pressure. (i.e.about 101 kPa), preferably greater than about 1 MPa, and more preferablygreater than about 5 MPa. The pressure in certain formation orprocessing plants or units could be much higher, say greater than about20 MPa. There is no specific high-pressure limit. The present method canbe used at any pressure that allows formation of hydrocarbon gashydrates.

The temperature of the condition for contacting is usually below, thesame as, or not much higher than the ambient or room temperature. Lowertemperatures tend to favor hydrate formation, thus requiring thetreatment with the composition of the present invention. At much highertemperatures, however, hydrocarbon hydrates are less likely to form,thus obviating the need of carrying out any treatments.

The ammonium, phosphonium, and sulphonium compounds of the presentinvention may also be connected through one of the organic side chains,such as represented by —R₄, to become a pendent group of manyoxygen-containing polymers. Such polymers include, but not limited topolyacrylate, polymethacrylate, copolymers of acrylate and methacrylate,polyacrylamide, polymethacrylamide, copolymers of acrylamide andmethacrylamide, and polymers and copolymers of N-vinylcaprctam.

The ammonium, phosphonium, and sulphonium compounds of the presentinvention may also be connected through one of the organic side chains,such as represented by —R₄, to become a pendent group of nitrogencontaining polymers, where the nitrogen is on the polymer backbone. Suchnitrogen containing polymers and copolymers can be obtained by theMichael addition reaction between polyethylenimine and acrylic ormethacrylic acids. The copolymers may also include N-vinylcaprolactam,N,N-dimethylacrylamide, N-ethylacrylamide, N-isopropylacrylamide,N-butylacrylamide, or N-tert. butylacrylamide. The suitable oniumcompounds can be attached through the acid moiety using suitable diaminoor aminoalcoholic chemicals followed by the salt forming reactions.

Based on the total weight of the composition, the concentration of theonium compound in a solvent should be in the range from about 5 wt % toabout 75 wt %, preferably from about 10 wt % to about 65 wt %.

In addition to the ammonium, phosphonium and sulphonium compounds, thecomposition may also include liquids. These liquids are generallysolvents for the virgin solid form of the compounds. Such solventsinclude, but are not limited to, water, simple alcohols like methanol,ethanol, iso-propanol, n-butanol, iso-butanol, 2-ethyl hexanol; glycolslike ethylene glycol, 1,2-propylene glycols, 1,3-propylene glycol, andhexylene glycol; ether solvents like ethylene glycol mono butylether(butyl cellosolve), ethylene glycol dibutyl ether, and tetrahydrofuran;ketonic solvents like methylethylketone, diisobutylketone,N-methylpyrrolidone, cyclohexanone; armatic hydrocarbon solvents likexylene and toluene; and mixtures thereof. The selection of the suitablesolvent or combination of solvents are important to maintain a stablesolution of the compounds during storage and to provide stability andreduced viscosity for the inhibitor solutions when they are injectedagainst a pressure of 200 to 25,000 psi. The solvent is present in theinhibitor composition in the range from 0% to about 95%, preferably from20% to about 95%, more preferably from 50% to about 95% of the totalcomposition, based on volume.

When the compounds of the present invention are added into the mixtureof hydrocarbons and water at any concentration effective to inhibit theformation of hydrates under the given conditions. Preferably, theconcentration of the active inhibitor compound is between about 0.01 wt% and about 5 wt % based on the water content. More preferably, theinhibitor compound concentration is between about 0.1 wt % and about 3wt %.

The present invention may also be used in combination with other meansof hydrate inhibition such as the use of thermodynamic or kineticinhibitors discussed in the background section. These other hydrateinhibitors may be of the same or different type of hydrate inhibitorused in the composition. If mixtures of hydrate inhibitors are used, themixture may be added to the hydrocarbon and water containing processstream through a single port or multiple ports. Alternatively,individual hydrate inhibitors may be added at separate ports to theprocess stream.

The present invention may also be used in combination with other oilfield flow assurance compounds such as, but not limited to, corrosioninhibitors, scale inhibitors, paraffin inhibitors, and asphalteneinhibitors. The hydrate inhibitors may also be used in combination withemulsion breakers or water clarifiers.

SIMPLE QUATERNARY AMMONIUM AND PHOSPHONIUM COMPOUNDS

Certain simple quaternary ammonium and phosphonium compounds aresuitable for inhibiting formation of gas hydrate plugs in conduitscontaining a mixture of hydrocarbons and water, by adding to the mixturean effective amount of at least one hydrate inhibitor compound. Onepreferred family of hydrate inhibitor compounds has the formula:

R₁ is selected from hydrogen and normal or branched alkyls having from 1to 3 carbon atoms.

R₂ is selected from normal or branched alkyls having from 1 to 4 carbonatoms, preferably exactly 4 carbon atoms. It should be recognized thatR₁ and R₂ may be the same or different, such as where R₁ and R₂ eachhave exactly one carbon atom.

R₃ is an organic moiety having 4 or 5 carbon atoms.

R₄ is an organic moiety having from 2 to 20 carbon atoms. In certainembodiments, R₄ may be selected from alkyl, alkenyl, aryl, arylalkyl,arylalkenyl, alkylaryl, alkenylaryl, glycol and combinations thereof.Alternatively, R₄ may include one or more heteroatoms selected fromoxygen, nitrogen, sulfur and combinations thereof. Still further, R₄ maybe chemically bound to a polymer. In one embodiment, R₄ is—[(CH₂—CHR₅—O)]_(n)—H, R₅ is selected from a hydrogen, a methyl group,an ethyl group, and combinations thereof, and n ranges from 1 to 3.

A is a nitrogen atom (N) or a phosphorus atom (P).

X⁻ is an anion. For example, X⁻ may be selected from hydroxide,carboxylate, halide, sulfate, organic sulphonate, and combinationsthereof. Suitably, the X⁻ anion may be a halide ion selected frombromide, chloride, and combinations thereof.

In one preferred embodiment, the at least one compound is the product ofa reaction between an organic halide having one of R₁, R₂, R₃, and R₄and an amine or phosphene having the other three of R₁, R₂, R₃, and R₄.For example, the at least one compound may be the product of a reactionbetween butyl bromide and an N,N-dimethyl-alkylamine having between 10and 20 carbon atoms. Suitably, the N,N-dimethyl-alkylamine may beN,N-dimethyl-hexadecylamine.

The method may be performed at any pressure, such as between 100 and10,000 psi or even greater than 10,000 psi.

Independently, the method may include adding at least one amine salt tothe mixture along with the at least one compound. For example, the aminesalt may include a cation moiety that is an amine selected from ammonia,dimethylamine, diethylamine, di-n-propylamine, trimethylamine,triethylamine, tri-n-propylamine, tri-iso-propylamine, ethanolamine,diethylethanolamine, triethanolamine, methyl ethanolamine, ethylethanolamine, propyl ethanolamine, methyl diethanolamine, ethyldiethanolamine, dimethyl ethanolamine, diethanolamine,dibutylethanolamine, dipropylethanolamine, dibutylpropanolamine,dipropylpropanolamine, morpholine, N-methylmorpholine,N-ethylmorpholine, N-propylmorpholine, dibutylethanolamine,N,N-dibutyl-cocoamidopropylamine, and combinations thereof.Alternatively, the amine salt may include an anionic moiety that is anacid selected from carboxylic acids and inorganic acids. Suitablecarboxylic acids include, with limitation, formic acid, acetic acid,propionic acid, butyric acid, glycolic acid, malonic acid, succinicacid, acrylic acid, methacrylic acid, trifluoroacetic acid, methanesulfonic acid and mixtures thereof. Suitable inorganic acids include,without limitation, nitric acid, hydrogen chloride, hydrogen bromide,and mixtures thereof.

Accordingly, the at least one compound may, for example, include atleast one of the following: dimethylbutylhexadecylammonium salt;dimethylbutyloctadecylammonium bromide, dimethylbutyldodecylammoniumsalt; at least one ammonium salt having an ammonium compound selectedfrom trimethylhexadecylammonium, dimethylethylhexadecylammonium,dimethylbutyloctadecylammonium, dimethylbutylhexadecylammonium,dimethylbutyldodecylammonium, dimethylbutyltetradecylammonium,propyldibutylhexadecylammonium, dipropylbutylhexadecylammonium, andmixtures thereof; or at least one phosphonium salt having a phosphoniumcompound selected from trimethylhexadecylphosphonium,dimethylethylhexadecylphosphonium, dimethylbutyloctadecylphosphoniumdimethylbutylhexadecylphosphonium, dimethylbutyldodecylphosphonium,dimethylbutyltetradecylphosphonium, propyldibutylhexadecylphosphonium,dipropylbutylhexadecylphosphonium, and mixtures thereof.

The hydrate inhibitor compound is preferably mixed with a solvent, forexample water, simple alcohols, glycols, ethers, ketonic liquids,aromatic hydrocarbons, and combinations thereof. More specifically,preferred solvents include water, methanol, ethanol, iso-propanol,n-butanol, iso-butanol, 2-ethyl hexanol, ethylene glycol, 1,2-prpyleneglycols, 1,3-propylene glycol, hexylene glycol, ethylene glycol monobutylether (butyl cellosolve), ethylene glycol dibutyl ether,tetrahydrofuran, methylethylketone, methylisobutylketone,diisobutylketone, N-methylpyrrolidone, cyclohexanone, xylene, toluene,and combinations thereof.

BETAINES AND AMINE OXIDES

Other quaternary ammonium and phosphonium compounds, known as betainesand amine oxides, have also been found to be suitable for inhibitingformation of gas hydrate plugs in conduits containing a mixture ofhydrocarbons and water, by adding to the mixture an effective amount ofat least one hydrate inhibitor compound having the formula:(R₁)(R₂)(R₃)A⁺—[R₄—(C═O)]_(m)—O⁻

In accordance with the invention, R₁, R₂, R₃ and R₄ are organicmoieties, wherein R₁ is an alkyl having 4 or 5 carbon atoms, R₂ ishydrogen or an alkyl having from 1 to 4 carbon atoms, and R₃ has 2 to 20carbon atoms. Optionally, R₃ has an amide functionality. In oneembodiment, R₃ is —[(CH₂—CHR₅—O)]_(n)—H, R₅ is selected from a hydrogen,a methyl group, and an ethyl group, and n ranges from 1 to 3. R₄ ispreferably a normal or branched alkyl group, such as where R₄ is—[CH₂—CHR₅)_(n)]—, n is 0 or 1, and R₅ is hydrogen or an alkyl havingfrom 1 to 3 carbon atoms.

A is N or P; and m is an integer 0 or 1.

The method may optionally include adding at least one amine salt to themixture along with the at least one compound. Suitable amine saltsinclude those previously described herein.

Preferred betaines may be derived from an amine and an acid, wherein theamine is selected from dibutylhexadecylamine, dibutyltetradecylamine,dibutyloctadecylamine, dibutyloleylamine, butyldicocoylamine, andmixtures thereof and the acid is selected from chloroacetic acid,acrylic acid, methacrylic acid, and mixtures thereof. Whether derived inthis or a different manner, suitable betaines include, withoutlimitation,

dibutylhexadecylcarboxypropyl, dibutyltetradecylcarboxypropyl,dibutyloctadecylcarboxypropyl, dibutyloleylcarboxypropyl,butyldicocoylcarboxypropyl, dibutylhexadecylcarboxyethyl,dibutyltetradecylcarboxyethyl, dibutyloctadecylcarboxyethyl,dibutyloleylcarboxyethyl, butyldicocoylcarboxyethyl,dibutylhexadecylcarboxymethyl, dibutyltetradecylcarboxymethyl,dibutyloctadecylcarboxymethyl, dibutyloleylcarboxymethyl,butyldicocoylcarboxymethyl and mixtures thereof. Suitable amine oxidesinclude, without limitation, butylmethylhexadecylamine,butylmethyltetradecylamine, butylmethyloctadecylamine,butylethylhexadecylamine, butylethyltetradecylamine,butylethyloctadecylamine, dibutylhexadecylamine, dibutyltetradecylamine,dibutyloctadecylamine, dibutyloleylamine, dibutylcocoylamine,butylpropylhexadecylamine, butylpropyltetradecylamine,butylpropyloctadecylamine, butylpropyloleoylamine, butyldicocoylamine,and mixtures thereof.

In one embodiment, at least one of R₁, R₂ and R₃ is the amide group—[(R₅—NH—(C═O)—R₆)], R₅ is selected from —(CH₂)_(t)—,—[CH₂—(CHR₇)_(t)]—, —(CH₂—CHR₇O)_(u)—(CH₂)_(t)— and combinationsthereof, wherein t is an integer 2 to 4, u is 0 or an integer (1 orgreater), R₇ is hydrogen or an alkyl having from 1 to 3 carbon atoms,and R₆ is an organic moiety, for example an alkyl or alkenyl group,having 4 to 20 carbon atoms. Most preferably, R₅ is—(CH₂—CHR₇O)_(u)—(CH₂)_(t)—.

A preferred method comprises adding to the mixture an effective amountof at least one compound having a formula:(R₁)(R₂)(R₃)A⁺—[R₄—(C═O)]_(m)—O⁻where: A is N or P; R₁ is an alkyl having 4 or 5 carbon atoms; R₂ ishydrogen or an alkyl having from 1 to 4 carbon atoms; R₃ is the amidegroup —[(R₅—NH—(C═O)—R₆)], wherein R₅ is selected from —CH₂)_(t)—,—[CH₂—CHR₇)_(t)]—, —(CH₂—CHR₇O)_(u)—(CH₂)_(t)— and combinations thereof,wherein, t is an integer 2 to 4, u is 0 or an integer (1 or greater), R₇is hydrogen or an alkyl having from 1 to 3 carbon atoms, and R₆ is anorganic moiety, such as an alkyl or alkenyl group, having 4 to 20 carbonatoms; R₄ is selected from —(CH₂)_(n)—, —[CH₂—(CHR₈)_(n)]— andcombinations thereof, wherein n is an integer 1 or greater and R₈ is analkyl having from 1 to 3 carbon atoms; and m is 0 or 1. In oneembodiment of this preferred method, m is 1 and R₄ is —CH₂)_(n)—. Whilen is an integer 1 or greater, n is preferably an integer from 1 to 10,more preferably from 2 to 4, and most preferably 2. R₅ is preferably—(CH₂—CHR₇O)_(u)—(CH₂)_(t)—, and R₇ is hydrogen, u is 0 or 1, and t ismost preferably 3. In one embodiment, R₁ and R₂ are butyl groups.

AMIDES

Further still, the method may include adding to the mixture an effectiveamount of at least one amide compound having a formula:

where: R₁, R₂, R₄, and R₅ are organic moieties; R₁ is an alkyl havingfrom 4 to 5 carbon atoms; R₂ is hydrogen or an alkyl having from 1 to 4carbon atoms; R₄ is selected from —(CH₂)_(t)—, —[CH₂(CHR₆)_(t)]—,—(CH₂—CHR₆O)_(u)—(CH₂)_(t)— and combinations thereof, wherein, t is aninteger 2 to 4, u is 0 or an integer (1 or greater) R₆ is hydrogen or analkyl having from 1 to 3 carbon atoms; R₅ is an organic moiety, such asan alkyl or alkenyl group, having 4 to 20 carbon atoms; A is N or P; X⁻is an anion; and a is 0 or 1. When a is 0, then R₃ is selected from—[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻,—[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, —[(CH₂)_(n) —(C═S)]—S⁻ and combinationsthereof, wherein n is 2 or 3, b is 0 or 1, c is 0 or 1, and R₆ isselected from hydrogen, methyl, ethyl and combinations thereof. When ais 1, then R₃ is selected from hydrogen and an organic moiety, such asan alkyl group, having from 1 to 20 carbon atoms, and combinationsthereof. Preferably, R₃ is the same group as the group containing theamide functionality, —R₄(NH)(C═O)R₅.

The X⁻ anion is preferably selected from hydroxide, carboxylate, halide,sulphate, organic sulphonate, and combinations thereof Suitable halideions include, without limitation, bromide, chloride, and combinationsthereof.

In one embodiment, R₃ is hydrogen, a is 1, and the anion X⁻ is selectedfrom hydroxide, carboxylate, halide, sulphate, organic sulphonate, andcombinations thereof. In a still further embodiment, the at least oneamide compound is the reaction product of an N,N-dialkyl-aminoalkylaminewith an ester or glyceride. Preferably, the ester or glyceride isderived from a plant source or an animal source selected from coconutoil, tallow oil, vegetable oil, and combinations thereof.

The method may further comprise adding at least one amine salt to themixture along with the at least one compound. Suitable amine saltsinclude those previously described herein. Furthermore, the at least onecompound may be mixed with the solvents previously described herein.

In another embodiment, the at least one compound includes a productprepared by the reaction of an amine selected from(3-dialkylamino)propylamine and (3-dialkylamino)ethylamine withvegetable oil or tallow oil followed by reacting with a reactantselected from an organic halide, for example an alkyl halide, havingfrom 4 to 20 carbon atoms, hydrogen peroxide, and an acid, wherein theacid is selected from mineral acids, formic acid, acetic acid,chloroacetic acid, propionic acid, acrylic acid, and methacrylic acid,and wherein the dialkyl of the (3-dialkylamino)propylamine includes twoalkyl groups independently selected from methyl, ethyl, propyl, butyl,morpholine, piperidine, and combinations thereof.

AMINO ALCOHOLS AND ESTER-1 COMPOUNDS

The present invention provides yet another method for inhibitingformation of gas hydrate plugs in conduits containing a mixture ofhydrocarbons and water. This method comprises adding to the mixture aneffective amount of at least one compound having a formula:

wherein: A is N or P; R₁ is a normal or branched alkyl group containingat least 4 carbon atoms; R₂ is hydrogen or an alkyl group containingfrom 1 to 4 carbon atoms; R₄ is selected from hydrogen, methyl andethyl; R₅ is either H or an organic moiety, such as an alkyl chain,containing from 4 to 20 carbon atoms; (X⁻)_(a) is an anion; a is 0 or 1;n is from 1 to 3; and m is 0 or 1. When a is 0, then R₃ is selected from—[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, —[(CH₂CH₂)—(SO₂)]—O⁻,—[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, and combinations thereof, wherein b is 0 or1; c is 0 or 1; and R₆ is selected from hydrogen, methyl, ethyl or acombination thereof. When a is 1, then R₃ is selected from hydrogen, anorganic moiety, for example an alkyl or alkenyl group, having from 2 to20 carbon atoms, and combinations thereof. The X⁻ anion is preferablyselected from hydroxide, carboxylate, halide, sulphate, organicsulphonate, and combinations thereof. The preferred halide ions include,without limitation, bromide, chloride, and combinations thereof.

The method may further comprise adding at least one amine salt to themixture along with the at least one compound. Suitable amine saltsinclude those previously described herein. Furthermore, the at least onecompound may be mixed with the solvents previously described herein.

In one embodiment, the at least one compound includes a product of thereaction of N-alkylamine or N,N-dialkylamine with ethylene oxide,propylene oxide or combinations thereof, followed by reacting with atleast one alkyl halide having from 1 to 20 carbon atoms.

In a further embodiment, the method comprises introducing ester moietiesby trans-esterfication of hydroxy terminals in the alkoxy chains usingmethyl esters of fatty acids.

ESTER-2 COMPOUNDS

The present invention provides still another method for inhibitingformation of gas hydrate plugs in conduits containing a mixture ofhydrocarbons and water. This method comprises adding to the mixture aneffective amount of at least one compound having a formula:

wherein: A is N or P; R₁ is an alkyl group containing at least 4 carbonatoms; R₂ is hydrogen or an alkyl group containing from 1 to 4 carbonatoms; R₄ is an organic moiety, for example an alkyl, alkenyl or arylgroup, containing from 4 to 20 carbon atoms, optionally 8 to 16 carbonatoms; (X)⁻ is an anion selected from hydroxide, chloride, bromide,sulfate, sulfonate, or carboxylate; and a is 0 or 1. When a is 0, thenR₃ is selected from —[(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻,—[(CH₂CH₂)—(SO₂)]—O⁻, —[(CH₂CH(OH)CH₂)-—(SO₂)]—O⁻, and combinationsthereof, wherein b is 0 or 1, c is 0 or 1; and R₆ is selected fromhydrogen, methyl, ethyl, and combinations thereof. When a is 1, then R₃is selected from hydrogen, an organic moiety, for example an alkyl oralkenyl group, having from 4 to 20 carbon atoms, and combinationsthereof.

In one embodiment, the at least one compound includes a product of theMichael addition reaction of alkyl or N,N-dialkyl amine with anacrylate, followed by reacting with at least one organic halide, such asan alkyl halide, having from 1 to 20 carbon atoms.

Optionally, the at least one compound includes a product of the reactionof a tertiary amine containing the ester moiety with chloroacetic acid,acrylic acid or methacrylic acid. In accordance with a similar option,the at least one compound includes a product of the reaction of atertiary amine containing the ester moiety with hydrogen peroxide.

EXAMPLE 1 Test Procedure for Evaluating Hydrate Inhibitor Compounds

The “Rocking Arm” test apparatus used for these evaluations contains“pressure cells” made of sapphire tubing containing a stainless steelball. The cells are placed in a rack, and the rack gently rockedforward, then back. The cells are charged with liquids prior to beingplaced in the rack and then immersed in an insulated tank containingwater. Once the cells are immersed in the bath they can then be chargedwith gas and the experiment begun. Sensors are used to monitor ballmovement within the cells, with one sensor placed near each end of thecell. The ball falling time is recorded. This data is referred to asSensor Activation Time and they are noted as Sensor-1 and Sensor-2.

In a typical experiment, the cells were charged with oil to brine ratiosranging from 10:1 to 1:10. A typical oil to brine ratio is about 2:1.The hydrate inhibitors were mixed with the solutions in the cells. Thecells were purged with a synthetic natural gas blend, then charged withgas to the desired pressure and allowed to equilibrate at thepre-determined temperature. The bath was then cooled to a lowerpre-determined temperature at specified rates. The following parameterswere recorded: (1) bath temperature, (2) individual cell pressure, (3)sensor activation time, and (4) visual observations. Hydrate formationor blockage is indicated by either an increase in sensor activation time(SAT) or visual observation of hydrate particles sticking to the walls.When evaluating the sensor data the results can indicate: (1) aviscosity increase due to the formation of hydrates, which can also bedue in part to oil effects; (2) a partial blockage; and (3) a completeblockage.

The inhibitor evaluations were conducted using a synthetic natural gasblend shown in Table 1. The composition of the synthetic salt water(brine) used for the inhibitor evaluations is presented in Table 2. Atypical temperature—pressure profile is presented in FIG. 1. A list ofinhibitor compounds that were evaluated and the results of theevaluations are summarized in Table 3 and in FIGS. 2-17. Each of theseinhibitor compounds was tested as an inhibitor solution at a 3 volume %dosage rate based on the amount of water in the mixture of hydrocarbonsand water. Each inhibitor solution was made up of 40 wt % inhibitorcompound and 60 wt % solvent, wherein the solvent itself was a mixtureof half xylene and half n-butanol. TABLE 1 Gas Composition SyntheticBlend Components Mol % Nitrogen 0.4 Methane 87.2 Ethane 7.6 Propane 3.1i-Butane 0.5 n-Butane 0.8 i-Pentane 0.2 n-Pentane 0.2

TABLE 2 Composition of Synthetic brine Concentrations of Individual IonsIons (mg/L) Sodium 24000 Potassium 250 Calcium 2800 Magnesium 990 Barium14 Strontium 95 Chloride 45019 Bromide 2200

TABLE 3 Inhibitor Compounds Evaluated Inhibitor Figure # InhibitorPerformance 2 None Complete hydrate blockage at 9° C. (48.2° F.). 3Trimethylhexadecylammonium Partial hydrate blockage at 6° C. (42.8° F.).bromide Later on, the hydrate broke lose. 4Dimethylethylhexadecylammonium Partial hydrate blockage at 4.4° C. (40°F.). bromide Later on, the hydrate broke lose. 5Dimethylbutylhexadecylammonium No hydrate blockage at 4.4° C. (40° F.)in bromide 18 hours. 6 Dimethylbutyloctadecylammonium No hydrateblockage at 4.4° C. (40° F.) in bromide 13 hours. 7Dipropylbutylhexadecylammonium No hydrate blockage at 4.4° C. (40° F.)in bromide 13 hours. 8 Dibutylpropylhexadecylammonium No hydrateblockage at 4.4° C. (40° F.) in bromide 13 hours.  9 a & bTributylhexadecylammonium bromide No hydrate blockage at 4.4° C. (40°F.) in 13 hours with 3% inhibitor; complete hydrate blockage with 1%inhibitor. 10  Dimethyldihexadecylammonium Complete hydrate blockage at11° C. bromide (51.8° F.). 11  N,N-Dibutyl-cocoamidopropyl No hydrateblockage at 4.4° C. (40° F.) in carbomethoxy betaine 13 hours. 12 N,N-Dibutylcocoamidopropylamine No hydrate blockage at 4.4° C. (40° F.)in oxide 13 hours. 13  N,N,N-Tributyl- No hydrate blockage at 4.4° C.(40° F.) in cocoamidopropylammonium bromide 13 hours. 14 N,N-Dibutylhexadecyl- No hydrate blockage at 4.4° C. (40° F.) incocoamidopropylammonium bromide 13 hours. 15 a & b N,N- No hydrateblockage at 4.4° C. (40° F.) in Dibutyltriethoxyhexadecylammonium 13hours with 1 and 3% inhibitor. bromide 16 a & bTributylhexadecylphosphonium No hydrate blockage at 4.4° C. (40° F.) inBromide 13 hours with 3% inhibitor; initial hydrate blockage with 1%inhibitor. 17 a & b Blend of N,N-Dibutyl- No hydrate blockage at 4.4° C.(40° F.) in cocoamidopropyl carboethoxy betaine 13 hours with 1 and 3%inhibitor. and amine salt

The above examples are intended to illustrate the performance of the newinhibitors. These examples are not intended and should not beinterpreted to limit their applicabilities under any other conditionssuch as pressure, gas composition, amount and type of oil, amount andtype of water (salinity). Please also note that the performance rankingof the inhibitors noted here may be changed or reversed under adifferent set of conditions.

The terms “comprising,” “including,” and “having,” as used in the claimsand specification herein, shall be considered as indicating an opengroup that may include other elements not specified. The term“consisting essentially of,” as used in the claims and specificationherein, shall be considered as indicating a partially open group thatmay include other elements not specified, so long as those otherelements do not materially alter the basic and novel characteristics ofthe claimed invention. The terms “a,” “an,” and the singular forms ofwords shall be taken to include the plural form of the same words, suchthat the terms mean that one or more of something is provided. Forexample, the phrase “a solution comprising a phosphorus-containingcompound” should be read to describe a solution having one or morephosphorus-containing compound. The terms “at least one” and “one ormore” are used interchangeably. The term “one” or “single” shall be usedto indicate that one and only one of something is intended. Similarly,other specific integer values, such as “two,” are used when a specificnumber of things is intended. The terms “preferably,” “preferred,”“prefer,” “optionally,” “may,” and similar terms are used to indicatethat an item, condition or step being referred to is an optional (notrequired) feature of the invention.

The disclosure of a range of values, such as a disclosure of a compoundhaving an alkyl having from 6 to 20 carbon atoms, shall be construed asfurther specifically disclosing each and every individual value therebetween, such as 7, 8, 9, . . . 18, 19. Where an embodiment is disclosedas including more than one range, then the disclosure shall be construedas further specifically disclosing each and every possible combinationof values within those ranges. Still further, the disclosure of lists ofalternative components, conditions, steps, or aspects of the inventionshall be construed as specifically disclosing each and every combinationof those alternatives, unless the combination is specifically excludedor mutually exclusive.

It should be understood from the foregoing description that variousmodifications and changes may be made in the preferred embodiments ofthe present invention without departing from its true spirit. It isintended that this foregoing description is for purposes of illustrationonly and should not be construed in a limiting sense. Only the languageof the following claims should limit the scope of this invention.

1. A method for inhibiting formation of gas hydrate plugs in conduitscontaining a mixture of hydrocarbons and water, the method comprising:adding to the mixture an effective amount of at least one compoundhaving a formula selected from:

where: R₁, R₂, R₄, and R₅ are organic moieties; R₁ is an alkyl havingfrom 4 to 5 carbon atoms; R₂ is hydrogen or an alkyl having from 1 to 4carbon atoms; R₄ is selected from —(CH₂)_(t)—, —[CH₂-(CHR₆)_(t)]—,—(CH₂-CHR₆O)_(u)—(CH₂)_(t)— and combinations thereof, wherein t is aninteger 2 to 4, u is 0 or an integer, R₆ is hydrogen or an alkyl havingfrom 1 to 3 carbon atoms; R₅ is an alkyl or alkenyl group having 4 to 20carbon atoms; A is N or P; X⁻ is an anion; and a is 0 or 1; wherein if ais 0, then R₃ is selected from —[(CH2)(CHR₆)_(b)(C═O)]_(c)—O⁻,—[(CH₂CH₂)—(SO₂)]—O⁻, —[(CH₂CH(OH)CH₂)—(SO₂)]—O⁻, —[(CH₂)_(n)—(C═S)]—S⁻and combinations thereof, n is 2 or 3, b is 0 or 1, c is 0 or1, and R₆ is selected from hydrogen, methyl, ethyl and combinationsthereof; and wherein if a is 1, then R₃ is selected from hydrogen,organic moieties having from 1 to 20 carbon atoms, and combinationsthereof.
 2. The method of claim 1, wherein, R₃ is hydrogen, a is 1, andthe anion X⁻ is selected from hydroxide, carboxylate, halide, sulphate,organic sulphonate, and combinations thereof.
 3. The method of claim 1,wherein [(CH₂)(CHR₆)_(b)(C═O)]_(c)—O⁻, and wherein a is 0; b is 0 or 1;c is 1; and R₆ is selected from hydrogen and a methyl group.
 4. Themethod of claim 1, wherein R₃ is —O⁻.
 5. The method of claim 1, whereinthe at least one compound is the reaction product of anN,N-dialkyl-aminoalkylamine with an ester or glyceride.
 6. The method ofclaim 5, wherein the ester or glyceride is derived from a plant sourceor an animal source selected from coconut oil, tallow oil, vegetableoil, and combinations thereof.
 7. The method of claim 1, wherein X⁻ isan anion selected from hydroxide, carboxylate, halide, sulphate, organicsulphonate, and combinations thereof.
 8. The method of claim 1, whereinthe X⁻anion is a halide ion selected from bromide, chloride, andcombinations thereof.
 9. The method of claim 1, further comprising:adding at least one amine salt to the mixture along with the at leastone compound.
 10. The method of claim 9, wherein the amine salt includesa cation moiety that is an amine selected from ammonia, dimethylamine,diethylamine, di-n-propylamine, trimethylamine, triethylamine,tri-n-propylamine, tri-iso-propylamine, ethanolamine,diethylethanolamine, triethanolamine, methyl ethanolamine, ethylethanolamine, propyl ethanolamine, methyl diethanolamine, ethyldiethanolamine, dimethyl ethanolamine, diethanolamine,dibutylethanolamine, dipropylethanolamine, dibutylpropanolamine,dipropylpropanolamine, morpholine, N-methylmorpholine,N-ethylmorpholine, N-propylmorpholine, dibutylethanolamine, andcombinations thereof.
 11. The method of claim 9, wherein the amine saltincludes an anionic moiety that is an acid selected from carboxylicacids and inorganic acids.
 12. The method of claim 9, wherein the aminesalt includes an anionic moiety that is a carboxylic acid selected fromformic acid, acetic acid, propionic acid, butyric acid, glycolic acid,malonic acid, succinic acid, acrylic acid, methacrylic acid,trifluoroacetic acid, methane sulfonic acid and mixtures therteof. 13.The method of claim 9, wherein the amine salt includes an anionic moietythat is an inorganic acid selected from nitric acid, hydrogen chloride,hydrogen bromide, and mixtures thereof.
 14. The method of claim 1,wherein the at least one compound includes a product prepared by thereaction of an amine selected from (3-dialkylamino)propylamine and(3-dialkylamino)ethylamine with vegetable oil or tallow oil followed byreacting with a reactant selected from an alkyl halide having from 4 to20 carbon atoms, hydrogen peroxide, and an acid, wherein the acid isselected from mineral acids, formic acid, acetic acid, chloroaceticacid, propionic acid, acrylic acid, and methacrylic acid, and whereinthe dialkyl of the (3-dialkylamino)propylamine includes two alkyl groupsindependently selected from methyl, ethyl, propyl, butyl, morpholine,piperidine, and combinations thereof.
 15. The method of claim 1, whereinthe at least one compound is mixed with a solvents selected from water,simple alcohols, glycols, ethers, ketonic liquids, aromatichydrocarbons, and combinations thereof.
 16. The method of claim 1,wherein the at least one compound is mixed with a solvents selected fromwater, methanol, ethanol, iso-propanol, n-butanol, iso-butanol, 2-ethylhexanol, ethylene glycol, 1 ,2-prpylene glycols, 1,3-propylene glycol,hexylene glycol, ethylene glycol mono butylether (butyl cellosolve),ethylene glycol dibutyl ether, tetrahydrofuran, methylethylketone,methylisobutylketone, diisobutylketone, N-methylpyrrolidone,cyclohexanone, xylene, toluene, and combinations thereof.
 17. The methodof claim 1, wherein R₃ is the same group as the —R₄(NH)(C═O)R₅ group.